With mine, as the temperature started to get higher and higher, the HDMI started dropping out. It would cause the monitor to blank out momentarily. It would stop late in the evening and be fine, but then during the day I would start seeing it again. Boosting the HDMI signal on the rpi didn’t help (in fact it made the temperature go up a bit higher even), but whenever I just blew across the rpi’s CPU, it would stop. That’s how I realized it was just getting too hot, even at the default speed. Now that I put it in a case with a fan, I haven’t had any issues.
